Field of the Invention
Embodiments of the invention generally relate to a segmented focus ring assembly for use in a plasma processing chamber.
Description of the Related Art
Continued evolution of the semiconductor requires smaller and smaller features to be patterned on substrates. As feature size shrinks, manufacturers are challenged to maintain control of device properties and performance. Maintaining control of critical dimensions of features on a semiconductor substrate is a fundamental requirement of etching processes used to form those features. During a plasma etch process, for example, the critical dimension (CD) could be the width of a gate structure, trench or via and the like.
As technology nodes advance and critical dimensions shrink, increasing emphasis is placed on reducing the amount of edge-exclusion on a substrate. Edge-exclusion refers to the area near the edge of a substrate in which no features or devices are formed. Reducing edge-exclusion provides space for forming additional devices nearer the edge of a substrate. As structures are formed closer to the edge, maintaining CD uniformity across the substrate during etching processes becomes more difficult. A common form of CD non-uniformity is known as “edge roll-off,” which features a dramatic reduction in CD control close to the edge of the substrate. Additionally, CD bias, the change in CD as successive layers are etched, declines near the edge.
Current plasma etch processes attempt to address this problem by providing a “focus ring” near the edge of the substrate that has similar composition to the substrate. It is thought that the focus ring behaves as an “extension” of the film being etched and promotes a uniform concentration of etch by-product species across the substrate. This, in turn, promotes a more uniform etch rate. However, in certain chamber designs, there is not enough room to accommodate a conventional focus ring.
Thus, there is a need for an alternative for conventional focus ring.